1. Field of the Invention
The present invention relates to a composition which has an accelerated mineral-absorbing effect and foods containing it. More specifically, it relates to a composition which contains minerals and poly-.gamma.-glutamic acid degraded product as a mineral-absorbance accelerating additive, and foods containing them.
2. Discussion of the Background
The human body comprises about 20 minerals, and of these Japanese people tend to be deficient in calcium, iron, zinc, copper, magnesium and other minerals, creating what is considered to be a dietary problem. In particular, the deficiencies are in calcium and iron.
In the case of calcium, the recommended daily allowances for adults has been set at 600 mg, and while the national average intake per capita is slightly lower at 540 mg (1989 national nutrition survey), a reduced intestinal absorption rate of calcium due to a variety of causes has led to the problem of calcium deficiency in the body. Osteoporosis, which occurs with high frequency among the elderly, is mainly related to a breakdown in the balance between calcium intake and excretion, and this becomes a major cause for the increase in bed-ridden elderly. Osteoporosis occurs with particularly high frequency among postmenopausal women, and one of the causes of this is thought to be the considerable lowering in secretion of female hormone (estrogen) and the lowering of the calcium absorption rate by the small intestine. The number of osteoporosis patients is increasing year by year, and is presently reported to be about 5 million.
In the case of iron, the recommended daily allowances for adults has been set at 11 mg (10 mg for men, 12 mg for women), and the national average intake per-capita is 11.4 mg (1989 national nutrition survey), barely fulfilling the recommended daily allowances as an average for men and women, while the problem of iron deficiency occurs particularly among menstruating women. It has been calculated that menstruating women excrete about twice the amount of iron per day as adult males, and thus the balance of iron in the body tends towards a lack thereof. The results of surveys reveal that 40-60% of menstruating women suffer from iron deficiency anemia.
Generally, it is considered that minerals must be present in the small intestine in a soluble state in order to be absorbed.
In the case of calcium, there are two routes for absorption, active transport controlled by the regulation of vitamin D and various hormones whereby calcium is absorbed in the upper small intestine against a concentration gradient, and passive transport whereby calcium in the lower small intestine is absorbed following a concentration gradient. However, when calcium is present in large amounts in the intestine, such as during the intake of food, the proportion of the passive transport from the lower small intestine is overwhelmingly high, and in contrast to the case of the active transport which cannot rise above a certain amount even if the concentration of calcium increases, the passive transport rises as the amount of the soluble calcium concentration in the intestine increases (Am. J. Physiol., 240, 32, 1981). In general, the rate of absorption of calcium in the intestines is reported to be 10-50%.
Iron is mainly absorbed in the upper small intestine, through the two modes of absorption of heme iron and nonheme iron. Whereas heme iron is absorbed as an iron porphyrin complex, nonheme iron is solubilized and liberated as a free ion before being absorbed (Gastroent., 58, 647, 1971). The absorption rate of iron is extremely low, being not greater than 10-20% for heme iron and 1%-5% for nonheme iron.
Casein phosphopeptide (CPP), a product of the enzymatic degradation of the milk protein casein, is an example of a substance which exhibits an accelerating effect on the absorption of calcium and iron by raising the concentrations of soluble calcium and soluble iron in the small intestine (Japanese Patent Publication No. HEI 02-7616, Japanese Patent Unexamined Publication No. SHO 59-162843). Calcium and iron are maintained in a soluble state by the chelating effect of the phosphate groups of phosphoserine and carboxyl groups of the acidic amino acids contained in CPP, which is therefore reported to produce an absorption accelerating effect thereon by increasing the concentrations of soluble calcium and soluble iron in the small intestine. However, the industrial production of CPP requires complicated procedures such as enzyme treatment, etc. , and when added to food, its degradation proceeds even further during the course of its movement through the small intestine, sometimes leading to a loss in its ability to solubilize minerals.
Even if casein is consumed directly, it is degraded enzymatically in the intestine, producing CPP, and therefore mineral absorption is accelerated. However, in this case as well, the degradation is promoted in the intestine sometimes leading to a loss in its ability to solubilize minerals, while casein has disadvantages from the point of view of food processing, such as poor solubility (particularly in the acidic range), etc.
Furthermore, foods are sometimes mineral-enriched using inorganic mineral salts or mineral powders, but these have the possibility of producing insoluble salts with other copresent substances, and since the excessive intake of one type of mineral inhibits the absorption of other minerals, there is not much improvement in the utilization of minerals in the body. For example, a large intake of calcium inhibits the absorption of iron. Excessive mineral-enrichment of foods is disadvantageous in that the taste of foods is spoiled by harsh, astringent, pungent taste produced by the minerals.
Poly-.gamma.-glutamic acid, present in the viscous substance of natto or secreted extracellularly by Bacillus bacteria such as Bacillus natto and the like, and synthetic poly-.alpha.-glutamic acid, both possess a solubilizing effect on minerals in the lower small intestine and accelerate mineral absorption (Japanese Patent Unexamined Publication No. HEI 03-30648) . However, when used as a material for food, since poly-.alpha.-glutamic acid is synthetic, there is a problem of safety, the production process is laborious, and like CPP it is sometimes degraded by proteases during movement through the intestine. Poly-.gamma.-glutamic acid present in the viscous substance of natto or poly-.gamma.-glutamic acid secreted by Bacillus natto bacteria such as Bacillus natto under normal culturing conditions both have a high viscosity, and therefore the labor required during their preparation and food processing treatment has been a disadvantage.